The overall objective of this proposed research is directed toward understanding the molecular events of sea urchin morphogenesis. The specific aim of this proposal is to employ a combination of immunological and recombinant DNA technologies to isolate genes that are specifically expressed in the mesoderm cell lineage of Strongylocentrotus purpuratus embryos. Gene products of particular interest are cytoskeletal proteins and cell surface components. Both classes of proteins may function in the cell movements and changes in cell/cell contacts that are characteristic of the micromere/primary mesenchyme/spicule morphogenic pathway. Briefly the approach entails construction of cDNA libraries in expression vectors and identifying mesoderm specific genes represented and expressed in these libraries by screening with monoclonal antibodies prepared against mesoderm specific proteins. Representative cDNA clones will be analyzed in terms of their developmental patterns of RNA and protein expression and their genomic DNA sequence organization. Tests of potential function of mesoderm specific gene products are also planned. The experiments are directed at obtaining new information concerning three issues of major importance in developmental biology: (i) molecular events of differentiation in a cell lineage whose fate is determined at a much earlier time, (ii) the relationship of specific genes expressed in the mesoderm lineage to maternal RNA sequences, (iii) the role of cell movements and cell/cell contacts during mesoderm ontogeny. These experiments will also provide detailed information on the structure and location of potential regulatory elements around genes that are specifically expressed in a major cell lineage. In addition a molecular analysis of sea urchin mesoderm ontogeny could provide a model system for mesodermal interactions in other developing systems.